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Reeves, Edmond Geoffrey David

Publications and source records attributed to Reeves, Edmond Geoffrey David.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

L -Value and Energy Dependence of 0.1–50 keV O + , He + , and H + Ions for CME and CIR Storms Over the Entire Van Allen Probes Era

Our studies report the first observation of L -value and energy sorted correlation of differential fluxes of 0.1–50 keV O + , He + , and H + ions with different geophysical parameters for 29 Coronal Mass Ejected (CME) and 40 Corotating Interaction Region (CIR)-driven geomagnetic storms during the entire Van Allen Probes era. For both solar wind drivers, ions with ≥1 keV energies show more variability in response to the solar wind changes, while the lower energy (<1 keV) ions are relatively stable. During the in-storm interval, O + ions show maximum flux enhancement and become further prominent during CME storms. O + ion (≥10 keV) fluxes show good correlation with – $V_{sw}B_z$, and Sym-H index during CME-driven storms in the L ~2.5–5.5. Apart from this, the average duration of persistence ($\langleΔt\rangle$) for enhanced fluxes is higher for CIR-driven storms with $\langleΔt\rangle_{O^+}>\langleΔt\rangle_{He^+}>\langleΔt\rangle_{H^+}$ at E ≤ 50 keV in the L ~2.5–5.5. Moreover, the observed value of $\langleΔt\rangle_i$ (where $\textit{i}$ is O + , H + or He + ) increases with the increasing L . Further, we discuss the plausible mechanisms to provide a comprehensive overview of L -values and energy sorted O + , He + and H + ion dynamics for two different categories of solar wind drivers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Scattering by whistler-mode waves during a quiet period perturbed by substorm activity

We study the dynamics of radiation belt electrons during a 10-day quiet period perturbed by substorm activity and preceding a high-speed stream (HSS), aiming at a global description of the radiation belts in L-shell, L in [2, 6], and energy [0.1, 10] MeV. We combine Van Allen Probes observations and Fokker-Planck numerical simulations of pitch-angle diffusion. The Fokker-Planck model uses event-driven pitch angle diffusion coefficients from whistler-mode waves, built from the wave properties and the ambient plasma density measurements from the Van Allen Probes. We first find this event has some similar characteristics to regular quiet times previously studied; a widely extended plasmasphere within which we observe strong and varying whistler-mode waves. These ambient conditions lead to strong pitch-angle scattering, which contributes to the creation of a wide slot region as well as a significant decay of the outer radiation belts, which are observed and qualitatively well simulated. In addition, we find the substorm activity causes short duration (within ± 4h) decay of the plasma density and a lowering amplitude of the whistler-mode waves within the plasmasphere, both causing opposite effects in terms of pitch angle diffusion. This leads to a diminution of pitch-angle diffusion at the time of the main substorm activity. Conversely, whistler-mode waves become enhanced in the time periods between the substorm injections. All effects cumulated, we find an enhancement of pitch angle diffusion by whistler-mode waves above L~4.7 during the 10-day period. This directly relates to the combination of quietness and substorm activity which allows pitch angle diffusing of up to 1 MeV electrons in the outer belt. Relativistic electrons of 1–2 MeV remain trapped in the outer belt, from L~4.7 to L~5.2, forming, in both the observations and the simulations, a distinct pocket of remnant electrons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Evidence of Alfvenic Poynting Flux as the Primary Driver of Auroral Motion During a Geomagnetic Substorm

Geomagnetic substorms are major energy transfer events where energy stored in the Earth's magnetotail is released into the ionosphere. Substorm phenomena, including auroral activities, earthward Poynting flux, magnetic field dipolarization, etc, have been extensively studied. However, the complex interplay among them is not fully understood. In a fortuitous event on June 7, 2013, the twin Van Allen Probes (separated by 0.4 h in local time) observed bursts of earthward Alfvenic Poynting flux in the vicinity of the plasma sheet boundary layer (PSBL). The Poynting flux bursts correlate with enhancements of auroral brightness around the footpoints of both spacecraft. This indicates a temporal and spatial correlation between the auroral brightening and Poynting flux bursts, and that the auroral motion is directly linked to the perpendicular expansion of the Alfven wave. These observations suggest that the Alfvenic Poynting flux is a primary driver for the auroral electron acceleration. Furthermore, around the time of auroral brightening, a dipolarization was seen to propagate more than 4 h in local time during a 20 min period. The azimuthal phase speed of this dipolarization (2 deg/min) is too small to explain the azimuthal motion of the aurora (13.6 deg/min), but the dipolarization could be related to the generation of the Alfvenic Poynting flux through phase mixing at strong density gradients like those in the PSBL.

58 GEOSCIENCES↗
DOE OSTI2021

RBSP-ECT Combined Pitch Angle Resolved Electron Flux Data Product

We describe a new data product combining pitch angle resolved electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration’s Van Allen Probes. Here, we describe the methodology used to combine each of the data sets and produce a consistent set of pitch-angle-resolved spectra for the entire Van Allen Probes mission. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product offers researchers a consistent cross calibrated data set to explore the particle dynamics of the inner magnetosphere across a wide range of energies.

79 ASTRONOMY AND ASTROPHYSICS↗